Patent Document 1 proposes, as a method for using a bone-conduction speaker having a vibrating surface to be put on the tragus, adjusting by manual operation the pressure with which the vibrating surface is put on the tragus in order to adjust the proportions of cartilage-conducted sound information and air-conducted sound information according to the level of ambient noise (Patent Document 1). Patent Document 2 proposes conducting vibration generated by an actuator from a diaphragm to the human body, then conducting the vibration of the diaphragm from the wrist to a finger by bone conduction, and then putting the finger into the ear canal or the like so that an audio signal can be heard (Patent Document 2). In Patent Document 3, the present inventors propose converting, via a ring worn on a user's finger, an audio signal into cartilage-conducted vibration, which is then conducted to the finger. In this way, the audio signal in the form of vibration of the finger conducts, as cartilage-conducted sound, to the cartilage around the ear canal, producing air-conducted sound inside the ear canal so as to conduct to the eardrum, and partly conducting directly to the inner ear via the cartilage (Patent Document 3). Patent Document 4 proposes taking out a wrist watch attachment connected to a cable wound up on a cord reel inside a wrist watch-type mobile telephone, wearing the attachment on a fingertip, and putting the fingertip into the earhole so that vibration of a vibration-conducting device fitted to the wrist watch attachment is conducted directly to the ear (Patent Document 4). Patent Document 5 proposes, as an alerting device, an incoming-call sensing accessory for a mobile telephone in which a vibration-generating device that vibrates on detecting an incoming-call signal is built into an ornamental accessory such as a wristband (Patent Document 5).